1. Field of the Invention
The present invention relates to a polishing apparatus for polishing a workpiece such as a semiconductor wafer to a flat mirror finish, and more particularly to a polishing apparatus having a cover which prevents liquid on a turntable from being scattered.
2. Description of the Related Art
Recent rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. One of the processes available for forming such interconnections is photolithography. Though the photolithographic process can form interconnections that are at most 0.5 .mu.m wide, it requires that surfaces on which pattern images are to be focused by a stepper be as flat as possible because the depth of focus of the optical system is relatively small.
It is therefore necessary to make the surfaces of semiconductor wafers flat for photolithography. One customary way of flattening the surfaces of semiconductor wafers is to polish them with a polishing apparatus.
Conventionally, a polishing apparatus has a turntable and a top ring which rotate at respective individual speeds. A polishing cloth is attached to the upper surface of the turntable. A semiconductor wafer to be polished is placed on the polishing cloth and clamped between the top ring and the turntable. An abrasive liquid containing abrasive grains is supplied onto the polishing cloth and retained on the polishing cloth. During operation, the top ring exerts a certain pressure on the turntable, and the surface of the semiconductor wafer held against the polishing cloth is therefore polished by a combination of chemical polishing and mechanical polishing to a flat mirror finish while the top ring and the turntable are rotated.
After, for example, one or more semiconductor wafers have been polished, the polishing cloth is processed to recover its original polishing capability. Various processes have been and are being developed for restoring the polishing cloth, and are collectively called "ndressing". The polishing cloth is dressed in order to enable the polishing apparatus to perform a good polishing function at all times without undesired degradation of a polishing performance.
When polishing semiconductor wafers or dressing the polishing cloth, an abrasive liquid or a deionized water (pure water) is supplied onto the polishing cloth on the turntable in the vicinity of the top ring, and hence the abrasive liquid or the deionized water tends to be scattered around because the turntable and the top ring are rotated.
On the other hand, when the polishing apparatus is used in a clean room for manufacturing semiconductor devices, it is necessary to enclose the polishing apparatus by partition walls so that the abrasive liquid or the deionized water is not scattered in the clean room. However, since the scattered abrasive liquid or the like adheres to the partition walls, troublesome cleaning of the partition walls is required, and various equipments such as driving devices for the top ring and the dressing tool are adversely affected by the scattered abrasive liquid.